Turbocharger systems with direct turbine interfaces

ABSTRACT

Turbine assemblies and related turbocharger systems having direct turbine interfaces are provided. One exemplary turbine assembly includes a first turbine housing having an outlet portion defining a fluid outlet of a first turbine and a second turbine housing having an inlet portion defining a fluid inlet of a second turbine, wherein at least a portion of the outlet portion radially surrounds at least a portion of the inlet portion to provide a direct interface from the fluid outlet of the first turbine to the fluid inlet of the second turbine in an axial direction.

CROSS-REFERENCE TO RELATED APPLICATIONS

The subject matter described here is related to the subject matterdescribed in U.S. patent application Ser. No. ______ (attorney docket123.0021), filed concurrently herewith.

TECHNICAL FIELD

The subject matter described herein relates generally to flow controlsystems, and more particularly, to turbocharger systems with directturbine-to-turbine interfaces.

BACKGROUND

Turbocharger systems are frequently used to improve the efficiency ofinternal combustion engines. Two-stage turbocharger systems can be usedto further improve the engine efficiency over a single-stageturbocharger system including a single turbine and a single compressor.While use of two-stage turbocharger systems may be desirable inautomotive vehicles, for example, to achieve fuel economy targets orother environmental goals, the combination of the added financial costin conjunction with the size, packaging, assembly, or installationconstraints can be prohibitive. However, designers of turbochargersystems are often faced with competing concerns regarding the mass flowthrough the turbines involved with the particular application or otherfactors that could impact the performance or reliability of theturbocharger system while in use. Accordingly, it is desirable toprovide a two-stage or multi-stage turbocharger system that is capableof achieving the desired gas flow and related reliability or performancetargets while also reducing the size, packaging, assembly, installation,or other costs associated therewith.

BRIEF SUMMARY

Turbine assemblies and related turbocharger systems having directturbine interfaces are provided. An exemplary turbine assembly includesa first turbine housing having an outlet portion defining a fluid outletof a first turbine and a second turbine housing having an inlet portiondefining a fluid inlet of a second turbine, wherein at least a portionof the inlet portion radially surrounds at least a portion of the outletportion to provide a direct interface from the fluid outlet of the firstturbine to the fluid inlet of the second turbine in an axial direction.

An embodiment of one exemplary turbocharger system is also provided. Theturbocharger system includes a first compressor, a first turbine coupledto the first compressor and having a first common rotational axistherewith, a second turbine, and a second compressor coupled to thesecond turbine and having a second common rotational axis therewith,wherein the first common rotational axis and the second commonrotational axis are concentric. The outlet of the first turbine beinginserted within the inlet of the second turbine to provide a directfluid interface for gas flow from the first turbine to the secondturbine.

Another exemplary embodiment of a turbocharger system includes a firstcompressor and a radial turbine having a first turbine wheel coupled tothe first compressor via a first rotary shaft. The radial turbineincludes a first turbine housing defining a radial fluid inlet and anaxial fluid outlet. The turbocharger system also includes a secondcompressor and an axial turbine having a second turbine wheel coupled tothe second compressor via a second rotary shaft aligned with the firstrotary shaft in an axial direction. The axial turbine includes a secondturbine housing defining an axial fluid inlet, wherein at least aportion of an axial inlet portion of the second turbine housing radiallysurrounds at least a portion of an axial outlet portion of the firstturbine housing to provide a direct fluid interface between the axialfluid outlet and the axial fluid inlet. The turbocharger system alsoincludes a sealing structure hermetically sealing the portion of theaxial inlet portion to the first turbine housing.

In another exemplary embodiment, a turbine assembly includes a firstturbine housing having an outlet portion defining a fluid outlet of afirst turbine and a second turbine housing having an inlet portiondefining a fluid inlet of a second turbine, wherein at least a portionof the outlet portion radially surrounds at least a portion of the inletportion to provide a direct interface from the fluid outlet of the firstturbine to the fluid inlet of the second turbine in an axial direction.

In yet another embodiment, a turbocharger system includes a firstcompressor, a first turbine coupled to the first compressor and having afirst common rotational axis therewith, a second turbine, and a secondcompressor coupled to the second turbine and having a second commonrotational axis therewith, wherein the first common rotational axis andthe second common rotational axis are concentric. The second turbine hasan inlet inserted within an outlet of the first turbine to provide adirect fluid interface for gas flow from the first turbine to the secondturbine.

Another embodiment of a turbocharger system includes a first compressorand a radial turbine having a first turbine wheel coupled to the firstcompressor via a first rotary shaft. The radial turbine includes a firstturbine housing defining a radial fluid inlet and an axial fluid outlet.The turbocharger system also includes a second compressor and an axialturbine having a second turbine wheel coupled to the second compressorvia a second rotary shaft aligned with the first rotary shaft in anaxial direction. The axial turbine includes a second turbine housingdefining an axial fluid inlet, wherein at least a portion of an axialoutlet portion of the first turbine housing radially surrounds at leasta portion of an axial inlet portion of the second turbine housing toprovide a direct fluid interface between the axial fluid outlet and theaxial fluid inlet. The turbocharger system also includes a sealingstructure hermetically sealing the portion of the axial outlet portionto the second turbine housing.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the subject matter will hereinafter be described inconjunction with the following drawing figures, wherein like numeralsdenote like elements, and:

FIG. 1 is a cross-sectional view of a two-stage turbocharger system inone or more exemplary embodiments;

FIG. 2 is a cross-sectional view of a directly interfacing turbineassembly suitable for use in the turbocharger system of FIG. 1 in anexemplary embodiment;

FIG. 3 is an exploded cross-sectional view of the turbine assembly ofFIG. 2;

FIG. 4 is a cross-sectional view of another embodiment of a directlyinterfacing turbine assembly suitable for use in the two-stageturbocharger system of FIG. 1 in accordance with one or more exemplaryembodiments; and

FIG. 5 is a partial cross-sectional view of another embodiment of adirectly interfacing turbine assembly suitable for use in theturbocharger system of FIG. 1 in another exemplary embodiment.

DETAILED DESCRIPTION

Embodiments of the subject matter described herein relate toturbocharger systems that include serial coaxial turbine stages thatinterface directly with one another without reliance on any interveningcomponents. At least an end portion of the housing defining one of thefirst turbine outlet or the second turbine inlet radially circumscribes,encompasses, or otherwise surrounds at least a proximate end portion ofthe housing defining the other of the first turbine outlet or the secondturbine inlet inserted therein. In this regard, an inner surface of thesurrounding portion of the outer turbine housing directly face or areotherwise adjacent to the outer surface of the inserted portion of theinner turbine housing without any intervening components between thefacing surfaces. Thus, gas flow from the first turbine outlet flowsdirectly into the second turbine inlet without any intervening ducting,and accordingly, the turbines may be understood as directly interfacingwith one another. An additional sealing structure circumscribes orotherwise surrounds the end portion of one of the turbine housings, andthe sealing structure is joined or otherwise affixed to the turbinehousings in a manner that hermetically seals the turbine interface. Inexemplary embodiments, the sealing structure circumscribes the outerturbine housing and extends towards the other turbine to maintain theseal while accommodating axial mobility of the turbines with respect toone another. At the same time, it should be noted that the outer turbinehousing restricts radial mobility of the inner turbine housing, therebyensuring smooth gas flow substantially aligned in the axial direction atthe turbine interface.

In exemplary embodiments, the first turbine is a radial turbine and thesecond turbine is an axial turbine, with the rotational axes of therespective turbine wheels being concentrically aligned in an axialdirection. As described in greater detail below in the context of FIGS.2-3 and 5, in one or more embodiments, the inlet portion of the secondturbine housing radially surrounds the end portion of the outlet portionof the first turbine housing. In such embodiments, the second turbineinlet portion restricts radial displacement of the first turbine outletwith respect to the second turbine to maintain gas flow at the fluidinterface substantially aligned in the axial direction. At the sametime, the sealing structure may accommodate axial mobility of theturbines with respect to one another. In one or more alternativeembodiments, as described in greater detail below in the context of FIG.4, the outlet portion of the first turbine housing radially surroundsthe end portion of the inlet portion of the second turbine housing.Similarly, in such embodiments, the first turbine outlet portionrestricts radial displacement of the second turbine inlet with respectto the first turbine to maintain gas flow at the fluid interfacesubstantially aligned in the axial direction.

FIG. 1 depicts an exemplary embodiment of a two-stage turbochargersystem 100 that includes turbine assembly 120 having a direct fluidinterface between turbines 102, 112. In practice, the turbochargersystem 100 may be designed for and utilized with any sort of automotivevehicle, such as, for example, heavy-duty or performance vehicles tolight-duty vehicles. The exhaust manifold(s) receives exhaust gases fromthe cylinders of the vehicle engine, which are directed to one or morefluid inlets 101 of a first turbine 102. The fluid outlet 103 of thefirst turbine 102 interfaces directly with the fluid inlet 111 of asecond turbine 112, thereby providing a path for exhaust gas flow fromthe first turbine outlet 103 directly into the second turbine inlet 111,as described in greater detail below. The exhaust gases exiting theoutlet 113 of the second turbine 112 are directed to the vehicle exhaustsystem for further handling and venting, as appropriate.

By virtue of the so-called “series” configuration of the turbines 102,112, the pressure of the input exhaust gases at the first turbine inlet101 is greater than the pressure of the exhaust gases at the secondturbine inlet 111, and accordingly, the first turbine 102 mayalternatively be referred to herein as the high-pressure turbine whilethe second turbine 112 may alternatively be referred to herein as thelow-pressure turbine. In exemplary embodiments, the first turbine 102 isrealized as a radial turbine having its outlet 103 configured so thatthe exiting exhaust gases flow in a direction substantially aligned withthe axis of rotation for the first turbine wheel 104 (or substantiallyorthogonal to the plane of the turbine wheel). The second turbine 112 isrealized as an axial turbine having its axis of rotation substantiallyaligned with the axis of rotation of the first turbine 102. In thisregard, rotation axes of the turbines 102, 112 may be coaxially andconcentrically aligned.

In the illustrated embodiment, a first compressor 106 has its compressorwheel (or impeller) 107 mounted or otherwise coupled to the firstturbine wheel 104 on a common rotary shaft 105, and a second compressor116 has its impeller 117 mounted or otherwise coupled to the secondturbine wheel 114 on a common rotary shaft 115. Thus, both thecompressors 106, 116 and the turbines 102, 112 may be coaxially andconcentrically aligned about the longitudinal axis of the assembledturbocharger system 100. The second compressor 116 may be arranged toreceive inlet air (e.g., downstream of an air filter) for compression toprovide charge air for the vehicle engine, which, in turn, may beprovided to the first compressor 106 for further charging (e.g.,supercharging), either directly or indirectly via a cooling device(e.g., an intercooler). The charge air output from the first compressor106 may be further cooled by a charge air cooler before provision to theengine intake or inlet manifold.

FIGS. 2-3 depict cross-sectional views of the turbine assembly 120 inthe turbocharger system 100 of FIG. 1. As described above, the firstturbine 102 is realized as a radial turbine with a first turbine housing122 that includes a hollow or voided volute portion 124 about the firstturbine wheel 104 that defines a radial fluid inlet 101 to the firstturbine 102 that radially directs input exhaust gas flow towards theturbine wheel 104. The first turbine housing 122 also includes a hollowor voided outlet portion 126 that extends axially away from the turbinewheel 104 towards the second turbine 112 and defines an axial fluidoutlet 103 from the first turbine 102. The outer circumference (ordiameter) of the end (or exit) portion 128 of the outlet portion 126distal to the first turbine wheel 104 is less than the innercircumference (or diameter) of the adjacent end (or entry) portion 138of the second turbine inlet portion 134 distal to the second turbinewheel 114, so that the end portion 128 of the first turbine outlet 126is directly inserted within the second turbine inlet 134. In otherwords, the outer surface 125 of the end portion 128 of the first turbinehousing 122 directly faces or is otherwise immediately adjacent to theinner surface 135 of the entry portion 138 of the second turbine housing132.

In the illustrated embodiment, the inner surface 127 of the firstturbine outlet portion 126 is tapered away from the rotational axis ofthe first turbine wheel 104 so that the inner diameter (orcircumference) of the outlet portion 126 increases from the firstturbine wheel 104 towards the exit end 128 of the first turbine outlet126. However, in alternative embodiments, the inner diameter (orcircumference) of the outlet portion 126 may be maintained constant ordecrease downstream from the first turbine wheel 104. In exemplaryembodiments, the inner surface 127 of the first turbine outlet 126 iscontoured to conform or otherwise correspond to the contour of the outersurface of an axially-extending and substantially-conical stator portion144 disposed therein, whereby the inner surface 127 of the first turbineoutlet 126 and the conical portion 144 cooperatively define a diffuserthat adjusts the exhaust gas flow characteristics downstream of thefirst turbine 102. For the illustrated embodiment in FIGS. 2-3, theradial area of the diffuser (e.g., the area between inner surface 127and the conical portion 144) increases outwardly downstream of the firstturbine 102 towards the second turbine inlet 111 to reduce the Machnumber and also reduce the tangential velocity of the exhaust gas flowat the second turbine inlet 111. At the same time, the diffuser isdesigned to reduce or otherwise minimize pressure losses exhibited bythe exhaust gas flow at the second turbine inlet 111.

As described above, the second turbine 112 is realized as an axialturbine with the second turbine housing 132 including a hollow or voidedinlet portion 134 about the second turbine wheel 114 that defines thesecond turbine inlet 111 and extends in the axial direction towards thefirst turbine 102 to receive axially input exhaust gas flow. The innercircumference (or diameter) of the end (or entry) portion 138 of theinlet portion 134 distal to the second turbine wheel 114 is greater thanthe outer circumference (or diameter) of the facing exit portion 128 ofthe first turbine 102 to directly receive the exit portion 128 of thefirst turbine outlet 126. In this manner, at least a portion of thesecond turbine inlet portion 134 radially surrounds or otherwiseencompasses at least the outlet exit portion 128 of the first turbinehousing 122. The second turbine housing 132 also defines a radial outletportion 136 for providing the exhaust gas to a downstream vehicleexhaust system or the like.

The difference between the inner diameter of the second turbine entryportion 138 and the outer diameter of the first turbine exit portion 128that is radially surrounded by the second turbine entry portion 138 ischosen to provide a radial air gap 148 that accommodates fabrication,assembly, or installation tolerances. For example, the first turbineinlet 101 may be connected to the engine exhaust manifold(s), which isconnected to the engine block via the cylinder head. Thus, the engineblock provides physical support for the first turbine 102. Additionally,the second turbine 112 may also be physically supported by the engineblock, for example, by the second turbine housing 132 being connected tothe engine block via a separate mounting or support structure. As aresult, the turbines 102, 112 and the engine block may be configured ina ring-like arrangement, with the air gap 148 providing clearancebetween the mating portions 128, 138 of the turbines 102, 112 thataccommodates installation or assembly while also preventing the turbinehousings 122, 132 from contacting one another during operation. In thisregard, based on the rigidity of the turbine housings 122, 132 and anyother structures facilitating mounting the turbine housings 122, 132 tothe engine block, the dimension of the air gap 148 may then be chosenthat is unlikely to result in physical contact between the housings 122,132 during operation due to vibrations or the like. In exemplaryembodiments, the air gap 148 is chosen to be about 2 millimeters (plusor minus manufacturing and installation variations or tolerances).

In exemplary embodiment, the second turbine entry portion 138 radiallyoverlaps the first turbine exit portion 128 for a distance 147 in theaxial direction that discourages or otherwise reduces the likelihood ofgas flow at the fluid interface in a non-axial direction. As a result,the exhaust gas flow path at the direct fluid interface between the exitof the first turbine outlet 103 and the input to the second turbineinlet 111 is maintained substantially aligned with the coincidentturbine axes with minimal “leakage” flow within the air gap 148. Inother words, the input gas to the axial second stage turbine 112(neglecting the influence of the vane assembly 142) is substantiallyaligned with the rotational axis of the axial second stage turbine 112.The overlapping distance 147 also reduces the distance between mountingfeatures 129, 139 to be spanned by the sealing structure 150, asdescribed in greater detail below. Accordingly, the overlapping distance147 may be optimized for a particular application to achieve a desiredlength for the sealing structure 150 and desired flow characteristics atthe turbine interface for a particular axial length of the turbineassembly 120. Additionally, it is noted that in exemplary embodiments,each of the turbine housings 122, 132 are comprised of a substantiallyrigid or inflexible material, such that the second turbine entry portion138 would restrict or otherwise limit radial movement of the firstturbine 102 with respect to the second turbine 112 to the width of theair gap 148.

In the illustrated embodiment, the inner surface 135 of the secondturbine inlet portion 134 of the second turbine housing 132 between thesecond turbine wheel 114 and the first turbine exit 128 is contoured,machined, or otherwise configured to receive and retain the vaneassembly portion 142 of the stator assembly 140. For example, the innersurface 135 of the second turbine inlet portion 134 may include groovesor similar features 137 corresponding to the outer surface of the vaneassembly 142. In the illustrated embodiment, the inner surface 135 ofthe second turbine inlet portion 134 also includes a groove or similarfeature configured to receive or otherwise retain (both axially andradially outward) one or more retaining features 146 (e.g., one or moreretaining clips), which, in turn, retain the stator assembly 140axially. The vane assembly 142 includes a plurality of guide vanesconfigured to direct or otherwise influence the input exhaust gas flowbefore impacting the axial turbine wheel 114 to achieve a desiredoperation of the second turbine 112. In exemplary embodiments, the vaneassembly 142 includes a central (or interior) voided portion adapted toreceive an end of the diffuser cone 144, which, in turn, is mounted,affixed, or otherwise joined to the vane assembly 142 to provide aunitary stator assembly 140 housed within the second turbine inlet 111.In exemplary embodiments, an axial air gap is provided between the endportion 128 of the first turbine outlet portion 126 and the vaneassembly 142 to provide clearance so that the first turbine outlet endportion 128 does not contact the stator assembly 140 and/or the vaneassembly 142 during operation. As illustrated, at least a portion of thediffuser cone 144 extends into the first turbine outlet 103, and thediffuser cone 144 is radially circumscribed or otherwise surrounded byat least the exit portion 128 of the first turbine outlet 126. Theportion of the first turbine outlet 126 that radially encompasses thatportion of the diffuser cone 144 is itself radially circumscribed orotherwise surrounded by at least the entry portion 138 of the secondturbine inlet 134. In other words, at least a portion of the diffusercone 144 is overlapped radially by both the first turbine outlet portion126 and the second turbine inlet portion 134.

The overlapping portions of the first turbine outlet 126 and the secondturbine inlet 134 define the interface between the first turbine fluidoutlet 103 and the second turbine fluid inlet 111. In exemplaryembodiments, a sealing structure 150 is provided at the interfacebetween the turbine housings 122, 132 to hermetically seal the firstturbine fluid outlet 103 with the second turbine fluid inlet 111. Theillustrated sealing structure 150 is realized as a bellows-likestructure that overlaps or otherwise radially surrounds at least aportion of the entry portion 138 of the second turbine inlet 134 and atleast a portion of the first turbine outlet 126 axially adjacent to theentry portion 138 of the second turbine inlet 134. In one or moreembodiments, the sealing structure 150 extends longitudinally from thesecond turbine inlet 134 towards a feature 129 on the outer surface ofthe first turbine outlet 126 where the sealing structure 150 is joinedor otherwise affixed to the first turbine housing 122. For example, asillustrated, the outer surface of the entry portion 138 of the secondturbine inlet 134 may include a flange or similar physical feature 139for receiving a first end of the sealing structure 150 and the outersurface of the first turbine outlet 126 may include another flange orsimilar physical feature 129 for receiving the opposing end of thesealing structure 150, with the respective ends of the sealing structure150 being joined or otherwise affixed to the respective features 129,139 using fastening elements 152, 154.

In one embodiment, the fastening elements 152, 154 are realized asV-band clamps that compress the ends of the bellows sealing structure150 with the flanges 129, 139 on the turbine housings 122, 132 tohermetically seal ends of the sealing structure 150, and therebyhermetically the interface between the turbines 102, 112. That said,other types of fastening elements 152, 154 may be utilized, including,for example, Marman clamps, adhesives, or the like. In exemplaryembodiments, the sealing structure 150 is flexible and provides at leastsome elasticity in the axial direction so that the turbine housings 122,132 may move towards or away from one another axially withoutcompromising the exhaust gas flow input to the second turbine inlet 111,which is guided in the axial direction by virtue of the diffuser cone144 and the second turbine inlet 134 at the exit of the first turbineoutlet 126. It should be noted that in alternative embodiments, in lieuof or in addition to a sealing structure 150 surrounding and sealing theoverlap of the turbine housings 122, 132, a sealing structure may beprovided within the air gap 148 between the turbine housings 122, 132 tohermetically seal the fluid interface. In yet other embodiments, theends of the sealing structure 150 can be welded, glued, or otherwisejoined to the turbine housings 122, 132, in which case separatefastening elements may not be present in such embodiments.

In the illustrated embodiment, the outlet portion 126 of the firstturbine housing 122 extends in the axial direction from the turbinewheel 104 towards the second turbine 112 by a distance that is greaterthan the maximum axial dimension of the radial inlet portion 124. Inother words, the longitudinal dimension of the first turbine outletportion 126 in the axial direction is greater than the dimension of thefirst turbine inlet portion 124 in the axial direction, so that thefirst turbine outlet portion 126 extends from the turbine wheel 104beyond the inlet portion 124 to provide clearance for assembly with thesecond turbine housing 132. That said, in other embodiments, thelongitudinal dimension of the first turbine outlet portion 126 in theaxial direction may be less than the dimension of the first turbineinlet portion 124 in the axial direction.

FIG. 4 depicts another embodiment of a turbine assembly 400 suitable foruse as the turbine assembly 120 in the turbocharger system 100 ofFIG. 1. Various elements or features of the turbine assembly 400 of FIG.4 are similar to their counterparts described above in the context ofFIGS. 1-3, and accordingly, for the sake of brevity, such commonelements or features and related functionality will not be redundantlydescribed in the context of FIG. 4.

In the illustrated embodiment, the inlet portion 434 of the secondturbine housing 432 is inserted within the outlet portion 426 of thefirst turbine housing 422. In this regard, the inner diameter (orcircumference) of an end (or exit) portion 428 of the hollow or voidedoutlet portion 426 that extends axially towards the second turbine 412is greater than the outer diameter (or circumference) of the adjacentend (or entry) portion 438 of the second turbine inlet portion 43, sothat the entry end 438 of the second turbine inlet 434 is directlyinserted within the exit end 428 of the first turbine outlet 426. Thus,the outer surface of the entry portion 438 of the second turbine housing432 is directly facing or otherwise immediately adjacent to the innersurface of the exit portion 428 of the first turbine housing 422.

In the illustrated embodiment, the inner surface 425 of the firstturbine outlet portion 426 is aligned substantially parallel to therotational axis of the first turbine wheel 404 to define a flow path forthe exhaust gas within the first turbine outlet 426 that is parallel tothe rotational axis. A lip or similar recessed physical feature 427 forreceiving the second turbine inlet 434 is formed in the end portion 428of the first turbine outlet 426, and the inner circumference (ordiameter) defined by the inner surface 429 of the lip 427 is greaterthan the inner circumference (or diameter) defined by the inner surface425 of the remaining portion of the first turbine outlet 426. Inexemplary embodiments, a corresponding lip or similar physical feature437 for insertion within or otherwise mating with the lip 427 in theexit end 428 of the first turbine outlet 426 is formed in the entry end438 of the second turbine inlet 434. In this regard, the outercircumference (or diameter) defined by the outer surface of the inletlip 437 is less than the inner circumference (or diameter) defined bythe inner surface of the outlet lip 427 to provide a radial air gap,which accommodates installation or assembly while also preventing theturbine housings 422, 432 from contacting one another during operation.In a similar manner as described above, the outlet lip 427 overlaps theinlet lip 437 in the axial direction to discourage or otherwise reducethe likelihood of gas flow at the fluid interface in a non-axialdirection. In some embodiments, the facing surfaces of the matingfeatures 427, 437 may be contoured or otherwise configured to provide alabyrinthine air gap to minimize any “leakage” flow at the turbineinterface, which improves efficiency and reduces thermal stress on thesealing structure 450 that could otherwise be caused by exposure to therelatively high temperature exhaust gas. In exemplary embodiments, thelength of the inlet lip 437 in the axial direction is substantiallyequal to the length of the outlet lip 427. Physical contact between theinlet lip 437 with the outlet lip 427 restricts radial displacement ofthe second turbine 112 with respect to the first turbine 102, and also,restricts axial displacement of the second turbine 112 towards the firstturbine 102 (e.g., in the direction opposite the axial flow direction).Thus, during assembly, the turbines 102, 112 can be adjusted orrepositioned with respect to one another (e.g., while mounting to theengine block) without damaging the sealing structure 450.

In exemplary embodiments, the inner surface 435 of the second turbineinlet portion 434 at the entry end 438 is aligned substantially parallelwith the inner surface 425 of the first turbine outlet 426 to facilitatemaintaining a relatively smooth flow of exhaust gas exiting the firstturbine outlet 103 at the fluid interface with the second turbine inlet111 in the axial direction. Additionally, the first turbine outlet exitportion 428 restricts or otherwise limits radial movement of the secondturbine 412 with respect to the first turbine 402 to a negligibleamount, and as a result, the exhaust gas flow path at the exit of thefirst turbine outlet 103 is maintained substantially aligned with theaxial turbine rotational axis.

In the illustrated embodiment, the inner surface 435 of the secondturbine inlet portion 434 is tapered away from the rotational axis sothat the inner circumference (or diameter) of the inlet portion 434increases from the entry end 438 towards the second turbine wheel 414.In exemplary embodiments, the inner surface 435 of the second turbineinlet 434 is contoured to conform or otherwise correspond to thecontours of the outer surfaces of a diffuser cone portion 444 disposedtherein. As described above in the context of FIGS. 2-3, the diffusercone 444 is mounted, affixed, or otherwise joined to a stator assembly440 disposed within the second turbine inlet portion 434. In a similarmanner as described above, the diffuser cone 444, in concert with thecontours of the second turbine inlet surface 435, adjustscharacteristics of the exhaust gas flow while minimizing pressure losses(e.g., by attempting to maintain the pressure of the exhaust gas flow atthe vane assembly 442 at or near the pressure of the exhaust gasentering the second turbine inlet portion 434 from the exit end 428 ofthe first turbine outlet 426). As illustrated, at least a portion of thediffuser cone 444 extends into and is radially circumscribed orotherwise surrounded by at least the exit portion 428 of the firstturbine outlet 426, and at least a portion of the first turbine outletexit portion 428 that radially encompasses the diffuser cone 444 alsoradially circumscribes or otherwise surrounds at least a portion of thesecond turbine entry portion 438. In other words, at least a portion ofthe diffuser cone 444 is overlapped in the radial direction by both thefirst turbine outlet 426 and the second turbine inlet 434.

In a similar manner as described above, the overlapping portions of thefirst turbine outlet 426 and the second turbine inlet 434 define theinterface between the first turbine fluid outlet 103 and the secondturbine fluid inlet 111, and a sealing structure 450 is provided at theinterface to hermetically seal the first turbine fluid outlet 103 withthe second turbine fluid inlet 111. For example, a bellows-likestructure 450 that overlaps or otherwise radially surrounds at least aportion of the first turbine outlet exit 428 proximate the secondturbine 412 and extends longitudinally towards the second turbine 412 tooverlap, and thereby seal the turbine interface. In a similar manner asdescribed above, the outer surface of the exit portion 428 of the firstturbine outlet 426 may include a flange 453 for receiving a first end ofthe sealing structure 150 and the outer surface of the second turbineinlet 434 may include another flange 451 for receiving the opposing endof the sealing structure 450, with the respective ends of the sealingstructure 450 being joined or otherwise affixed to the respectiveflanges 451, 453 using fastening elements 452, 454 that seal the ends ofthe sealing structure 450.

In the illustrated embodiment, the outlet portion 426 of the firstturbine housing 422 extends in the axial direction from the turbinewheel 404 towards the second turbine 412 by a distance that is less thanthe maximum axial dimension of the radial inlet portion 424 of thehousing 422. In other words, the longitudinal dimension of the firstturbine outlet portion 426 in the axial direction is less than thedimension of the radial turbine inlet portion 424 in the axialdirection, so that the radial turbine inlet portion 424 extends from theturbine wheel 404 beyond the outlet portion 426 to reduce thelongitudinal dimension of the turbine assembly 400 in the axialdirection. That said, in other embodiments, the longitudinal dimensionof the first turbine outlet portion 426 in the axial direction may begreater than the dimension of the first turbine inlet portion 424 in theaxial direction.

FIG. 5 depicts a partial cross-sectional view of another embodiment of aturbine assembly 500 suitable for use as the turbine assembly 120 in theturbocharger system 100 of FIG. 1. Various elements or features of theturbine assembly 500 of FIG. 5 are similar to their counterpartsdescribed above in the context of FIGS. 1-3, and accordingly, for thesake of brevity, such common elements or features and relatedfunctionality will not be redundantly described in the context of FIG.5. The turbine assembly 500 is similar to the turbine assembly 120 ofFIGS. 1-3, however, the turbine assembly 500 differs in that the vaneassembly 142 of the stator assembly 140 is retained axially by aretaining structure 502 that is joined, mounted, or otherwise affixed tothe second turbine housing 532. The retaining structure 502circumscribes the end portion 128 of the first turbine outlet portion126 in a manner that does not influence the direct fluid interfacebetween the first turbine outlet 103 and the second turbine inlet 111.In exemplary embodiments, the retaining structure 502 includes a flange504 or similar feature that facilitates joining the retaining structureto the entry portion 538 of the second turbine housing 532 using afastening element 506, such as a clamp. In this regard, the retainingstructure 502 may be effectively hermetically sealed to the entryportion 538 of the second turbine housing 532 to prevent any fluid flowbetween the retaining structure 502 and the second turbine housing 532.The end of the sealing structure 150 proximate the second turbine 112 iswelded or otherwise joined to the retaining structure 502, while theother end of the sealing structure 150 is fastened to the first turbinehousing 122, in a similar manner as described above. Thus, the retainingstructure 502 and the sealing structure 150 cooperatively seal theinterface between the turbines 102, 112, with the retaining structure502 and the fastening element 506 cooperatively retaining the statorassembly 140 within the second turbine inlet 111.

For the sake of brevity, conventional techniques related to turbines,compressors, turbochargers, and other functional aspects of the systems(and the individual operating components of the systems) may not bedescribed in detail herein. Furthermore, the connecting lines shown inthe various figures contained herein are intended to represent exemplaryfunctional relationships and/or physical couplings between the variouselements. It should be noted that many alternative or additionalfunctional relationships or physical connections may be present in anembodiment of the subject matter.

The foregoing description may refer to elements or components orfeatures being “coupled” together. As used herein, unless expresslystated otherwise, “coupled” means that one element/node/feature isdirectly or indirectly joined to (or directly or indirectly communicateswith) another element/node/feature, and not necessarily mechanically.Thus, although the drawings may depict one exemplary arrangement ofelements, additional intervening elements, devices, features, orcomponents may be present in an embodiment of the depicted subjectmatter. In addition, certain terminology may also be used in thefollowing description for the purpose of reference only, and thus arenot intended to be limiting. For example, the terms “first,” “second,”and other such numerical terms referring to structures do not imply asequence or order unless clearly indicated by the context.

The foregoing detailed description is merely illustrative in nature andis not intended to limit the embodiments of the subject matter or theapplication and uses of such embodiments. As used herein, the word“exemplary” means “serving as an example, instance, or illustration.”Any implementation described herein as exemplary is not necessarily tobe construed as preferred or advantageous over other implementations.Furthermore, there is no intention to be bound by any theory presentedin the preceding background, brief summary, or the detailed description.

While at least one exemplary embodiment has been presented in theforegoing detailed description, it should be appreciated that a vastnumber of variations exist. It should also be appreciated that theexemplary embodiment or exemplary embodiments are only examples, and arenot intended to limit the scope, applicability, or configuration of thesubject matter in any way. Rather, the foregoing detailed descriptionwill provide those skilled in the art with a convenient road map forimplementing an exemplary embodiment of the subject matter. It should beunderstood that various changes may be made in the function andarrangement of elements described in an exemplary embodiment withoutdeparting from the scope of the subject matter as set forth in theappended claims. Accordingly, details of the exemplary embodiments orother limitations described above should not be read into the claimsabsent a clear intention to the contrary.

What is claimed is:
 1. A turbine assembly comprising: a first turbinehousing having an outlet portion defining a fluid outlet of a firstturbine; and a second turbine housing having an inlet portion defining afluid inlet of a second turbine, wherein at least a portion of theoutlet portion radially surrounds at least a portion of the inletportion to provide a direct interface from the fluid outlet of the firstturbine to the fluid inlet of the second turbine in an axial direction.2. The turbine assembly of claim 1, wherein the first turbine comprisesa radial turbine and the second turbine comprises an axial turbine. 3.The turbine assembly of claim 2, wherein rotational axes of the radialturbine and the axial turbine are concentrically aligned in the axialdirection.
 4. The turbine assembly of claim 3, further comprising astructure to provide a seal between the portion of the outlet portionand the second turbine housing.
 5. The turbine assembly of claim 2, thefirst turbine housing having a second inlet portion defining a radialfluid inlet, wherein a first dimension of the outlet portion extendingtowards the second turbine in the axial direction is less than a seconddimension of the second inlet portion in the axial direction.
 6. Theturbine assembly of claim 1, wherein an inner surface of the portion ofthe outlet portion is adjacent to an outer surface of the portion of theinlet portion in a radial direction orthogonal to the axial direction.7. The turbine assembly of claim 1, wherein an inner surface of theoutlet portion of the first turbine includes a recessed feature forreceiving the inlet portion of the second turbine.
 8. The turbineassembly of claim 7, wherein an outer surface of the inlet portionincludes a second recessed feature corresponding to the recessedfeature, wherein contact of the second recessed feature with therecessed feature restricts displacement of the second turbine withrespect to the first turbine.
 9. The turbine assembly of claim 1,further comprising a structure to provide a seal between the portion ofthe outlet portion and the second turbine housing.
 10. The turbineassembly of claim 9, wherein the structure is flexible in the axialdirection.
 11. The turbine assembly of claim 9, wherein: an outersurface of the inlet portion includes a first feature; an outer surfaceof the outlet portion includes a second feature; a first end of thestructure is joined to the first feature; and a second end of thestructure is joined to the second feature.
 12. The turbine assembly ofclaim 1, further comprising a stator assembly housed within the inletportion of the second turbine, the stator assembly including a diffusercone portion extending from the second turbine in the axial directioninto the fluid outlet.
 13. The turbine assembly of claim 12, wherein theportion of the outlet portion radially surrounds at least a portion ofthe diffuser cone portion and the portion of the inlet portion isdisposed between the portion of the diffuser cone portion and theportion of the outlet portion.
 14. The turbine assembly of claim 12,wherein an inner surface of the inlet portion is contoured to correspondto a portion of the diffuser cone portion disposed within the fluidinlet.
 15. A turbocharger system comprising: a first compressor; a firstturbine coupled to the first compressor and having a first commonrotational axis therewith; a second turbine having an inlet insertedwithin an outlet of the first turbine to provide a direct fluidinterface for gas flow from the first turbine to the second turbine; anda second compressor coupled to the second turbine and having a secondcommon rotational axis therewith, wherein the first common rotationalaxis and the second common rotational axis are concentric.
 16. Theturbocharger system of claim 15, further comprising a sealing structurehermetically sealing the inlet of the second turbine with the outlet ofthe first turbine.
 17. The turbocharger system of claim 16, wherein thesealing structure comprises a bellows structure expandable in an axialdirection aligned with the first and second common rotational axes. 18.The turbocharger system of claim 17, wherein the outlet of the firstturbine restricts displacement of the inlet of the second turbine in aradial direction orthogonal to the axial direction.
 19. The turbochargersystem of claim 15, further comprising a stator assembly disposed withinthe inlet of the second turbine, wherein the stator assembly includes adiffuser cone portion extending into the outlet of the first turbine.20. A turbocharger system comprising: a first compressor; a radialturbine having a first turbine wheel coupled to the first compressor viaa first rotary shaft, the radial turbine comprising a first turbinehousing defining a radial fluid inlet and an axial fluid outlet; asecond compressor; an axial turbine having a second turbine wheelcoupled to the second compressor via a second rotary shaft aligned withthe first rotary shaft in an axial direction, the axial turbinecomprising a second turbine housing defining an axial fluid inlet,wherein at least a portion of an axial outlet portion of the firstturbine housing radially surrounds at least a portion of an axial inletportion of the second turbine housing to provide a direct fluidinterface between the axial fluid outlet and the axial fluid inlet; anda sealing structure hermetically sealing the portion of the axial outletportion to the second turbine housing.